Sound propagation near tunnel outlets

This paper investigates the noise propagation in a tunnel by both normal mode and boundary element methods. The analysis of the sound field close to the tunnel outlet is the main concern of this study, since the pressure of sound varies abruptly in this region. The boundary element method is used to construct numerical solutions in this study for convenience. On the other hand, a theoretical analysis of axisymmetric solutions inside circular pipes with an inclined flange. based on the three-dimensional wave equation and the normal mode method, is set up to verify the numerical results. The convergence of the analytical solutions and the accuracy of the numerical approach are tested for different pipe-radii and wavelength ratios. Finally, the boundary element method, with an approximated radiation condition, is used to simulate a tunnel noise field.